Stainless Steel Sheet for Structural Components Excellent in Impact Absorption Property

ABSTRACT

This invention provides a steel sheet for structural components excellent in impact absorption property comprising, in mass %, C: 0.005 to 0.05%, N: 0.01 to 0.30%, Si: 0.1 to 2%, Mn: 0.1 to 15%, Ni: 0.5 to 8%, Cu: 0.1 to 5%, Cr: 11 to 20%, Al: 0.01 to 0.5%, and a balance of Fe and unavoidable impurities, wherein Md 30  value given by equation (A) is 0 to 100° C., and total impact energy absorption in dynamic tensile testing is 500 MJ/m 3  or greater: 
       Md 30 =551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)   (A).

FIELD OF THE INVENTION

This invention relates to a stainless steel sheet used chiefly instructural components requiring strength and impact absorptioncapability, and particularly to a stainless steel sheet for automobileand bus impact absorption components such as front side members, pillarsand bumpers, and for structural components such as vehicle suspensionmembers and rims, railcar bodies and the like.

DESCRIPTION OF THE RELATED ART

Environmental concerns have in recent years made improvement of the fueleconomy of cars, motorcycles, buses, railcars and other means oftransport a critical issue. One aggressively-pursued approach toboosting fuel economy has been car body weight reduction. Car bodyweight reduction relies heavily on lowering the weight of the materialsused to fabricate the body components, specifically on reducing thethickness of sheet steels. However, sheet metal thickness reduction hasthe undesirable effect of degrading rigidity and collision (crash)safety performance. As strength enhancement of the steels used forcomponent fabrication is an effective way to increase collision safety,ordinary steels and high-strength steels are utilized in automobileimpact absorption components. Ordinary steels are, however, poor incorrosion resistance and multi-coat coating is essential for their use.They cannot be used for unpainted or lightly painted components, andmulti-coat painting increases cost. Although ordinary steels can beimparted with high strength by various methods such as solutionhardening, precipitation hardening, dual phasing, anddeformation-induced transformation, all of the methods aredisadvantageous in the point that the strengthening is accompanied by amarked decline in ductility. As ductility declines, fabrication into thestructural component becomes increasingly difficult, so that the degreeof structural freedom is greatly degraded.

Cr-containing stainless steels are far superior to ordinary steels incorrosion resistance and are therefore viewed as having the potential toreduce weight by lowering the corrosion margin (extra thickness tocompensate for expected corrosion) and to eliminate the need forpainting. In addition, austenitic stainless steels are excellent instrength-ductility balance and are considered capable of achieving highstrength in combination with high ductility through chemical compositionadjustment. Moreover, as regards collision safety improvement, utilizinga steel having high impact absorption capability in the vehicle framemakes it possible, for example, to absorb crash impact by componentcollapse deformation and thus to lessen the impact on passengers duringa collision. In other words, considerable merits can be realizedregarding fuel economy improvement through body weight reduction,painting simplification and safety enhancement.

Austenitic stainless steels such as SUS301L and SUS304 are used in thestructural components of railcars, for instance, because they areexcellent in corrosion resistance, ductility and formability. JapanesePatent Publication (A) No. 2002-20843 teaches an austenitic stainlesssteel with high strain rate and excellent impact absorption capabilitythat is intended for use mainly in structural components and reinforcingmaterials for railcars and ordinary vehicles. This is a steel containing6 to 8% Ni and having an austenite structure that achieves high strengthduring high-speed deformation owing to the formation ofdeformation-induced martensite phase. This prior art defines thedeformation strengths under dynamic deformation and static deformation,maximum strength, work-hardening index and other properties of thesteel. However, it is inadequate on the point of impact energyabsorption, which is the most important aspect from the viewpoint ofsafety at the time of sustaining a high-velocity impact, and even thoughthe difference between dynamic deformation strength and staticdeformation strength may be great, collision performance may be inferiorif the static deformation strength is low. The dynamic/static ratio isdefined as the ratio between the maximum dynamic and static strengths.But strength, e.g., yield strength, in the relatively low strain rangeis strongly affected by the impact absorption property at the time ofcollision, so the definition based on the maximum strength ratio maybecome a problem in some cases. Moreover, when deformation occurs duringa collision, not only strength but also steel ductility may be acontributing factor, and this has necessitated a design taking heavydeformation reaching the point of destruction into consideration as anabsorbed energy property. In other words, the teaching of JapanesePatent Publication (A) No. 2002-20843 is insufficient regarding safetyperformance at the time of collision, namely, impact absorptionproperty. In addition, the inclusion of a relatively large amount of Nimakes cost high, so that application to automobiles, motorcycles, busesand other ordinary transportation vehicles has been difficult.

Further, martensitic stainless steel sheets imparted with high strengthby quenching (e.g., SUS420) have very low ductility and are extremelypoor in weld toughness. Since automobiles, buses and railcars have manywelded structures, their structural reliability is greatly impaired bypoor weld toughness. On the other hand, ferritic stainless steel sheets(e.g., SUS430) are low in strength and not suitable for membersrequiring strength, and they are incapable of improving collision safetyperformance owing to their low impact energy absorption at the time ofhigh-velocity deformation.

SUMMARY OF THE INVENTION

Thus no technology has been available for enabling a vehicle structuralcomponent made of stainless steel sheet to achieve good collision safetyperformance by improving its impact energy absorption during high-speeddeformation, while simultaneously ensuring good formability of thestainless steel sheet. The present invention is directed to overcomingthe foregoing issues by providing a stainless steel sheet that is bothhigh in strength and excellent in impact absorption property duringhigh-speed deformation.

The inventors carried out a study on metal structure in relation todeformation mechanism at the time of sustaining high-speed deformation.As a result, they discovered a technique that enables improvement ofimpact energy absorption during high-speed deformation of an austeniticstainless steel while simultaneously achieving excellent sheetworkability. Specifically, for increasing deformation resistance duringultra-high speed deformation of a strain rate of 10³/sec,deformation-induced transformation is positively exploited to increasework hardenability, thereby increasing impact energy absorption througha dramatic improvement in strength and ductility when the componentcollides. Therefore, a vehicle body fabricated using the steel sheetabsorbs the impact at the time of a collision and minimizes bodycollapse, thereby markedly increasing the safety of passengers.

The gist of the present invention is as set out in the following.

A steel sheet for structural components excellent in impact absorptionproperty comprising, in mass %, C: 0.005 to 0.05%, N: 0.01 to 0.30%, Si:0.1 to 2%, Mn: 0.1 to 15%, Ni: 0.5 to 8%, Cu: 0.1 to 5%, Cr: 11 to 20%,Al: 0.01 to 0.5%, and a balance of Fe and unavoidable impurities,wherein Md₃₀ value given by equation (A) is 0 to 100° C., and totalimpact energy absorption in dynamic tensile testing is 500 MJ/m³ orgreater:

Md₃₀=551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)   (A).

(2) The steel sheet for structural components excellent in impactabsorption property according to (1), wherein dynamic/static ratio ofyield strength is 1.4 or greater.

(3) The steel sheet for structural components excellent in impactabsorption property according to (1) or (2), wherein tensile strength is600 MPa or greater and elongation at break is 40% or greater in statictensile testing.

(4) A steel sheet for structural components excellent in impactabsorption property comprising, in mass%, C: 0.005 to 0.05%, N: 0.01 to0.30%, Si: 0.1 to 2%, Mn: 0.1 to 15%, Ni: 0.5 to 8%, Cu: 0.1 to 5%, Cr:11 to 20%, Al: 0.01 to 0.5%, and a balance of Fe and unavoidableimpurities, wherein Md₃₀ value given by equation (A) is 0 to 100° C.,and impact energy absorption to 10% strain in dynamic tensile testing is50 MJ/m³ or greater:

Md₃₀=551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)   (A).

(5) The steel sheet for structural components excellent in impactabsorption property according to (4), wherein dynamic/static ratio ofyield strength is 1.4 or greater.

(6) The steel sheet for structural components excellent in impactabsorption property according to (4) or (5), wherein tensile strength is600 MPa or greater and elongation at break is 40% or greater in statictensile testing.

(7) The steel sheet for structural components excellent in impactabsorption property according to (4) or (5), wherein tensile strength is700 MPa or greater and elongation at break is 5% or greater in statictensile testing.

“Total impact energy absorption in dynamic tensile testing” is definedas the impact energy absorption up to break when a high-velocity tensiletest is conducted at a strain rate of 10³/sec corresponding to that atthe time of a vehicle collision, and “impact energy absorption to 10%strain” is defined as the impact energy absorption up to the 10% strainregion in the high-velocity tensile test. The static tensile test is atensile test conducted at the usual strain rate (strain rate of10^(−3 to −2)/sec).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the relationship between Md₃₀ value andtotal impact energy absorption in high-speed tensile testing.

FIG. 2 is a diagram showing the relationship between Md₃₀ value andimpact energy absorption to 10% strain in high-speed tensile testing.

DETAILED DESCRIPTION OF THE INVENTION

The reasons for the limitations of the invention are explained in thefollowing.

The important point in the present invention is the impact absorptionupon incurring a high-speed impact. The impact force at the time of avehicle collision is applied to structural components of the vehicle.The impact absorption capability of the steel constituting thecomponents is therefore important. Up to now, no attempt has been madeto provide a stainless steel that takes into account the impact energyabsorption at high strain rate and high speed, nor has vehicle designwith this in mind been carried out. Most vehicle structural componentshave angular cross-sections as typified by hat-shaped formed components.Although the strain region that absorbs impact differs among differentstructural components, what is important at locations that collapseduring collision is the impact energy absorption up to materialdestruction. Total impact energy absorption is therefore used as anindex. Total impact energy absorption improves as both strength andductility are higher during high-speed deformation. However,conventional high-strength steel sheet, while high in strength, is lowin fracture ductility and is therefore limited in total energyabsorption.

The present invention improves collision safety performance to theutmost from the material standpoint by utilizing high ductility and highwork hardenability property during deformation to dramatically improvetotal energy absorption. Moreover, since some locations need to absorbimpact up to the 10% strain region, i.e., a relatively low strain rateregion, impact energy absorption to strain rate of 10% is adopted as anindex. Although this depends on the component shape, it applies toautomobile front side member regions and the like, as indicated in“Report on Research Group Results Regarding High-Speed Deformation ofAutomotive Materials” (compiled by The Iron and Steel Institute ofJapan, p 12).

The larger is the ratio between yield strength in static tensile testingand yield strength in dynamic tensile testing, the more preferable foran impact absorption structural member. Moreover, a steel with highductility is preferable for fabrication into vehicle structuralcomponents. The elongation at break in static tensile testing wastherefore used as a general material index.

The inventors carried out a study based on the foregoing indexes, bywhich they learned that that the optimum stainless steel in terms ofexcellent impact absorption property is an austenitic stainless steelutilizing work hardening by deformation-induced transformation. Theyfurther learned that desired impact energy absorption during high-speeddeformation can be achieved by adjusting the various constituents tocontrol austenite so that deformation-induced martensite transformationoccurs suitably during high-speed deformation.

Austenite stability constituting an index of deformation-inducedmartensite transformation is calculated based on Md₃₀ value shown below(from the Stainless Steel Handbook compiled by the Japan Stainless SteelAssociation). The Md₃₀ value is the temperature at which 50% ofmartensite is formed at the time of imparting tensile strain to a truestrain of 0.3. When impact energy absorption was assessed using thisvalue, it was found that the excellent impact energy absorptionprescribed by the present invention could be obtained.

Md₃₀=551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)−18.5Mo−68Nb.

When Mo and Nb are not contained, the foregoing Md₃₀ becomes that of thefollowing equation (A):

Md₃₀=551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)   (A).

Explanation will be made first regarding the steel composition.

C must be added to a content of 0.005% or greater to achieve highstrength. On the other hand, C content is defined as 0.05% or less,because addition of a large amount degrades formability and weldability.Taking refining cost and grain boundary corrosion property into account,the more preferable content range is 0.01 to 0.02%.

N, like C, is effective for strength enhancement and beneficial forimproving impact energy absorption. For these purposes, it must be addedto a content of 0.01% or greater. On the other hand, N content isdefined as 0.30% or less, because excessive addition degradesformability and weldability. Taking refining cost, manufacturability andgrain boundary corrosion property into account, the more preferablecontent range is 0.015 to 0.025%.

Si is a deoxidizing element that is also a solution hardening elementeffective for achieving high strength. For these purposes, it must beadded to a content of 0.1% or greater. On the other hand, Si content isdefined as 2% or less, because addition of a large amount degradesformability and markedly lowers the dynamic/static ratio. Takingmanufacturability into account, the more preferable content range is 0.2to 1%.

Mn is a deoxidizing element and a solution hardening element effectivefor achieving high strength. Mn also promotes work hardening ofaustenite phase during high-speed deformation. For these purposes, itmust be added to a content of 0.1% or greater. On the other hand, Mncontent is defined as 15% or less, because when added in a large amount,deformation-induced martensite is not formed and formation of MnS, whichis a water-soluble inclusion, degrades corrosion resistance. Takingdescaling property in the manufacturing process into account, the morepreferable content range is 1 to 10%.

Ni is an element that improves corrosion resistance. For this, and foraustenite phase formation, Ni must be present at a content of 0.5% orgreater. On the other hand, Ni content is defined as 8% or less, becausewhen added in a large amount, raw material cost is markedly higher anddeformation-induced martensite is not formed. Taking manufacturability,stress corrosion cracking and the like into account, the more preferablecontent range is 1.5 to 7.5%.

Cu improves formability and contributes to dynamic/static ratioimprovement. It is added to a content of 0.1% or greater. Cu alsoproduces its effects when included from scrap or the like in thecomposition adjustment process. When added in excess of 5%, however,deformation-induced martensite formation no long occurs, so the contentis defined as 5% or less. The more preferable range is 0.1 to 4%.

Cr is an important element that must be added to a content of 11% orgreater from the viewpoint corrosion resistance. On the other hand, theupper limit of Cr addition is defined as 20%, because excessive additionnecessitates addition of large amounts of other elements for structureregulation. The content range is preferably 14 to 18%.

Al is added as a deoxidizing element and also because it renderssulfides harmless and contributes to improvement of workability aspectssuch as hole expandability during component processing. These effectsappear at an Al content of 0.01% or greater, so the lower limit ofcontent is defined as 0.01%. The upper content limit is defined as 0.5%,because addition in excess of this level leads to surface flawoccurrence and manufacturability degradation. Taking cost and the likeinto account, the more preferable content range is 0.1 to 0.5%.

When the material is impacted, it manifests deformation-inducedtransformation that transforms austenite phase into martensite phase,thereby effectively giving rise to work hardening during deformation.The efficient formation of martensite phase during deformation causeshigh strengthening and also prevents necking, thereby contributing toductility improvement. Since martensite transformation is affected bystrain and temperature, martensite formation is inhibited by the heat ofdeformation generated during high-speed deformation. However, in thestainless steel sheet of the present invention, it was found thatmartensite formation at the initial stage of deformation is sometimespromoted more during dynamic deformation than during static deformation.This is attributable to the strain rate dependence of transformationdependent on composition and the effect thereof dramatically improvesimpact energy absorption during high-speed deformation.

Various stainless steel sheets (thickness; 1.5 mm) were subjected todynamic tensile testing at a strain rate of 10³/sec. The effect of Md₃₀value on total impact energy absorption and impact energy absorption to10% strain at this time are shown in FIGS. 1 and 2, respectively.

It can be seen that within the range of the present invention both totalimpact energy absorption and impact energy absorption to 10% strainexhibit excellent values. When Md₃₀ value is too high, ductility isthought to be lowered because cracking occurs at the boundary betweenaustenite phase and martensite phase owing to excessive formation ofmartensite during deformation. Heretofore, total impact energyabsorption at the time of high-speed deformation of high-strength steelhas been thought to be on the order of less than 400 MJ/m³ (see, forexample, CAMP-ISIJ, Vol 9 (1996), P 1101, FIG. 4 and Symposium onAutomobile Materials, Japan Stainless Steel Association, 1997, p 71).

The present invention provides a steel having much higher impactabsorption property than the conventional high-strength steel, whereinthe total impact energy absorption is defined as 500 MJ/m³ or greaterand, from FIGS. 1 and 2, the range of Md₃₀ value is defined as 0 to 100°C. In the Md₃₀ value range of the present invention, the impact energyabsorption to 10% strain obtained is 50 MJ/m³ or greater. Studiesconducted by the inventors showed that if impact energy absorption of 50MJ/m³ can be obtained, that is adequate as the impact absorptionproperty in the relatively low strain region. So the impact energyabsorption to 10% strain is defined as 50 MJ/m³ or greater. No upperlimit value is defined for the impact energy absorption because theeffect of the present invention can be realized without defining one.

The dynamic/static ratio is an index representing the deformation ratedependence of work hardening. It is the ratio of yield strength indynamic tensile testing to yield strength in static tensile testing andis here defined specifically as (yield strength in dynamic tensile testwhen conducting dynamic tensile testing at strain rate of10³/sec)/(yield strength when conducting static tensile testing atstrain rate of 10⁻²/sec) . Since the dynamic/static ratio indicates thedegree of hardening at the time of deformation at high speed as in anautomobile collision, the suitability of a steel for use in an impactabsorption structural component increases in proportion as the value ofthe dynamic/static ratio increases. For example, “Report on ResearchGroup Results Regarding High-Speed Deformation of Automotive Materials”(compiled by The Iron and Steel

Institute of Japan, 2001, p 12, FIG. 6) gives dynamic/static ratios forconventional steels, with the dynamic/static ratio of a steel having atensile strength of 600 MPa or greater shown as 1.3 or less. The presentinvention defines the dynamic/static ratio as 1.4 or greater andprovides a steel of high strength and high dynamic/static ratiounattainable by conventional steels. No upper limit value is defined forthe dynamic/static ratio because the effect of the present invention canbe realized without defining one.

The stainless steel of the present invention is intended for fabricationinto structural components. It is therefore important for it to havegood formability. As pointed out earlier, most vehicle structuralcomponents have angular cross-sections as typified by hat-shaped formedcomponents. As the fabrication involves bending and drawing, the steelrequires ductility. A study was carried out regarding methods offabricating impact absorption components. It was found with regard tosteel for which tensile strength was 600 MPa or greater in statictensile testing, adequate forming was possible if elongation at breakwas 40% or greater. Elongation at break in static tensile testing wastherefore defined as 40% or greater. Some components require highstrength of 700 MPa or greater. Such high-strength steels are adjustedin strength by cold rolling and annealing followed by temper rolling.Although no upper limit of strength is necessary from the materialaspect, the upper limit is defined as 1600 MPa in view of manufacturingand practical concerns. When temper rolling is conducted, the reductioncan be set in accordance with the required strength level. However,taking manufacturability into consideration, it is preferably around 1to 70%. The steel sheet manufactured in this manner is reduced inelongation at break in static tensile testing. However, the elongationat break in static tensile testing of a steel sheet of the foregoingtensile strength level is required to be 5% or greater. It is thereforedefined as 5% or greater and is preferably 10% or greater.

The method of manufacturing the steel sheet of the present invention isnot particularly defined and the product thickness can be decided basedon requirements. The hot rolling conditions, hot rolled sheet thickness,hot rolled sheet and cold rolled sheet annealing temperature andatmosphere, and other matters can be suitably selected. No specialequipment is required in connection with the pass schedule, cold rollingreduction and roll diameter in cold rolling, and efficient use ofexisting equipment suffices. Use/non-use of lubricant during temperrolling, the number of temper rolling passes and the like are also notparticularly specified. If desired, shape correction utilizing a tensionleveler can be applied after cold rolling and annealing or after temperrolling. Although the product structure is fundamentally austenite,formation of a second phase, such as of ferrite or martensite, is alsoacceptable.

EXAMPLES

The present invention will be concretely explained in the following withreference to working examples.

Steels having the chemical compositions shown in Table 1 were producedand cast into slabs. Each slab was hot rolled, annealed, pickled, coldrolled to a thickness of 1.5 mm, annealed, pickled, and temper rolled toobtain a product sheet. The so-obtained product sheet was subjected tothe aforesaid static tensile test and dynamic tensile test.

Table 1 includes examples corresponding to claims 1 to 6. The steelshaving chemical compositions prescribed by the present invention weresuperior to the comparison steels in both total impact energy absorptionto destruction and impact energy absorption in the low strain region to10% strain, so that that they were excellent in impact absorptionproperty. Such steels are suitable for use in impact absorptioncomponents at risk of experiencing relatively large deformation Thesteels were also suitable for formation into complex structural members,as evidenced by their high elongation at break and excellent ductilityin static tensile testing.

Table 2 includes examples corresponding to claim 7. The inventionexamples, whose temper rolling reduction was adjusted to achieve tensilestrength of 700 MPa or greater and elongation at break is 5% or greater,exhibited high impact energy absorption to 10% strain of 50 MJ/m³ orgreater in dynamic tensile testing, as well as a dynamic/static ratio of1.4 or greater, making them suitable for use in high-strength membersrequired to absorb impact in the low strain region.

TABLE 1 Static yield Md₃₀ strength No. C Si Mn Ni Cr Cu Al N (° C.)(MPa) Invention 1 0.020 0.6 1.1 7.1 17.4 0.2 0.03 0.129 16 364 Examples2 0.023 0.5 8.6 5.0 14.5 2.5 0.03 0.046 29 280 3 0.030 0.6 1.5 5.1 17.71.0 0.02 0.131 41 325 4 0.029 0.6 1.5 6.1 17.7 1.0 0.05 0.129 12 312 50.021 0.5 1.0 7.4 17.3 0.2 0.02 0.115 18 319 6 0.019 0.5 3.4 3.6 17.33.5 0.03 0.122 12 330 7 0.021 0.5 6.6 3.5 17.4 0.2 0.03 0.118 82 378 80.022 0.5 6.0 3.5 17.4 2.4 0.01 0.120 23 345 9 0.021 0.5 3.4 3.6 17.21.5 0.02 0.119 73 359 10 0.021 0.5 3.4 3.5 17.1 2.0 0.04 0.119 60 363 110.021 0.5 3.4 5.2 17.1 2.0 0.03 0.117 12 317 12 0.021 0.5 6.3 3.5 17.21.0 0.07 0.122 62 352 13 0.021 0.5 6.3 3.5 17.1 1.5 0.03 0.121 50 346 140.025 0.5 3.5 3.5 17.3 0.2 0.02 0.210 65 362 15 0.020 0.3 6.5 3.5 17.30.2 0.01 0.240 31 367 16 0.015 0.5 6.5 3.5 17.6 1.0 0.04 0.240  4 321 170.009 0.8 3.5 1.0 17.3 3.5 0.04 0.210 47 331 18 0.045 0.5 11.0  0.8 19.50.5 0.05 0.280  2 335 19 0.006 0.9 11.6  3.1 11.5 0.5 0.05 0.280 55 367Comparative 20 0.004 0.5 0.3 0.1 10.5  0.04 0.03 0.007 391  228 Examples21 0.057 0.5 0.2 0.1 16.2  0.02 0.03 0.009 289  308 22 0.003 0.1 0.1 0.116.6  0.02 0.02 0.010 313  210 23 0.007 0.4 1.0 0.1 18.3  0.02 0.050.013 277  351 24 0.346 0.8 0.6 0.2 13.4  0.02 0.02 0.019 180  408 250.016 0.5 0.7 7.2 25.4  0.05 0.03 0.144 −91  717 26 0.055 0.4 1.1 8.118.1  0.19 0.03 0.041  6 301 27 0.051 0.6 0.9 9.1 18.2  0.18 0.01 0.015−11 273 28 0.008 0.4 2.7 7.9 17.1 2.7 0.02 0.012 −26  175 29 0.048 0.50.9 12.6  16.8  0.26 0.04 0.032 −99  306 30 0.085 0.5 11.4  6.6 17.9 0.10 0.03 0.302 −163  448 31 0.040 0.4 1.1 6.4 17.4 2.2 0.07 0.059  4292 32 0.021 0.5 1.0 3.6 17.3  0.21 0.03 0.116 129  997 33 0.020 0.5 3.53.5 17.4 0.2 0.02 0.118 108  401 34 0.026 0.9 1.8 7.1 16.0 1.9 0.010.010 33 266 35 0.021 0.5 1.0 5.2 17.3  0.21 0.04 0.116 82 722 36 0.0200.5 1.0 3.6 17.2 3.6 0.04 0.121 30 757 37 0.020 1.6 1.1 7.2 17.4 0.20.05 0.129  5 476 38 0.020 0.8 18   7.3 16.2 0.2 0.03 0.030 −65  235 390.020 0.8 18   0.2 16.2 7.3 0.02 0.030 −65  216 Total Static StaticDynamic Total impact elongation tensile yield impact energy to Dynamic/at break strength strength energy 10% strain static No. (%) (MPa) (MPa)(MJ/m³) (MJ/m³) ratio Invention 1 55 745 687 541 56 1.9 Examples 2 54796 516 517 55 1.8 3 41 826 576 594 54 1.8 4 55 700 670 535 56 2.1 5 56710 640 571 56 2.0 6 55 682 670 523 56 2.0 7 51 806 740 545 61 2.0 8 50649 678 508 54 2.0 9 46 834 736 558 56 2.1 10 44 637 678 528 55 1.9 1160 637 650 503 52 2.1 12 58 712 710 523 53 2.0 13 56 715 728 508 56 2.114 47 1013  688 532 62 1.9 15 53 816 692 519 56 1.9 16 54 722 650 512 592.0 17 62 882 635 506 53 1.9 18 50 715 670 550 55 2.0 19 46 856 610 57665 1.7 Comparative 20 36 398 550 256 46 2.4 Examples 21 31 480 514 27447 1.7 22 37 384 489 251 40 2.3 23 31 520 672 267 47 1.9 24 25 642 661282 54 1.6 25 26 806 889 408 81 1.2 26 50 682 547 525 48 1.8 27 52 628427 510 37 1.6 28 52 507 380 475 31 2.2 29 45 622 473 486 45 1.5 30 44785 1008  550 72 2.3 31 58 617 505 173 47 1.7 32  9 1265  1287  207 901.3 33 26 1013  722 583 49 1.8 34 54 673 356 511 37 1.3 35 21 1146 1234  440 89 1.7 36 20 1118  1261  348 66 1.7 37 36 950 533 505 43 1.138 50 374 310 436 41 1.3 39 53 362 285 415 38 1.3 Remarks: Chemicalconstituents are expressed in mass %. Underlining indicates that valueis outside invention range.

TABLE 2 Total Temper Static Static Static Dynamic impact rolling yieldelongation tensile yield energy to Dynamic/ reduction strength at breakstrength strength 10% strain static No. (%) (MPa) (%) (MPa) (MPa)(MJ/m³) ratio Invention 1 2 399 54 710 57 1.8 Examples 1 10 656 33 925998 59 1.5 1 20 739 30 985 1120 81 1.5 1 44 1106 12 1263 1612 82 1.5 160 1412  5 1502 1970 83 1.4 6 20 753 32 1005 1180 80 1.6 7 1 405 53 795780 57 1.9 7 20 758 31 1035 1180 84 1.6 7 45 1200 15 1295 1685 90 1.4 155 405 35 800 743 60 1.8 16 15 735 30 905 1064 73 1.4 Comparative 1 751535  1 1615 2010 48 1.3 Examples 6 75 1580  4 1820 2040 45 1.3 7 721593  2 1850 2053 44 1.3 8 80 1635  1 1686 1964 40 1.2 16 85 1785  11765 2035 32 1.1 Remark: Underlining indicates that value is outsideinvention range.

As is clear from the foregoing explanation, the present inventionenables provision of a high-strength stainless steel sheet excellent inimpact absorption capability even without addition of large amounts ofalloying elements. The stainless steel sheet manifests outstandingindustrial usefulness, including environmental protection through weightreduction and improved collision safety, especially when utilized in thestructural components of transport means such as automobiles, buses andrailcars.

1. A steel sheet for structural components excellent in impactabsorption property comprising, in mass %: C: 0.005 to 0.05%, N: 0.01 to0.30%, Si: 0.1 to 2%, Mn: 0.1 to 15%, Ni: 0.5 to 8%, Cu: 0.1 to 5%, Cr:11 to 20%, Al: 0.01 to 0.5%, and a balance of Fe and unavoidableimpurities, wherein Md₃₀ value given by equation (A) is 0 to 100° C.,and total impact energy absorption in dynamic tensile testing is 500MJ/m³ or greater:Md₃₀=551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)   (A).
 2. The steel sheetfor structural components excellent in impact absorption propertyaccording to claim 1, wherein dynamic/static ratio of yield strength is1.4 or greater.
 3. The steel sheet for structural components excellentin impact absorption property according to claim 1, wherein tensilestrength is 600 MPa or greater and elongation at break is 40% or greaterin static tensile testing.
 4. A steel sheet for structural componentsexcellent in impact absorption property comprising, in mass %: C: 0.005to 0.05%, N: 0.01 to 0.30%, Si: 0.1 to 2%, Mn: 0.1 to 15%, Ni: 0.5 to8%, Cu: 0.1 to 5%, Cr: 11 to 20%, Al: 0.01 to 0.5%, and a balance of Feand unavoidable impurities, wherein Md₃₀ value given by equation (A) is0 to 100° C., and impact energy absorption to 10% strain in dynamictensile testing is 50 MJ/m³ or greater:Md₃₀=551−462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)   (A).
 5. The steel sheetfor structural components excellent in impact absorption propertyaccording to claim 4, wherein dynamic/static ratio of yield strength is1.4 or greater.
 6. The steel sheet for structural components excellentin impact absorption property according to claim 4, wherein tensilestrength is 600 MPa or greater and elongation at break is 40% or greaterin static tensile testing.
 7. The steel sheet for structural componentsexcellent in impact absorption property according to claim 4, whereintensile strength is 700 MPa or greater and elongation at break is 5% orgreater in static tensile testing.